Some new insights into the formation of equine enteroliths
A horse owner in Louisville, Kentucky was feeding her senior Arabian gelding one evening in the stall and heard the distinct ”clacking” sound of rock pebbles hitting one another. To her surprise, she saw about twenty 1-2 cm stones in her horse’s poop! What she had just witnessed was quite rare, especially in the eastern part of the U.S. – the passing of stones called enteroliths from her horse’s colon! Normally stones of this size would go unnoticed in the pasture. Enteroliths are more common in the west and southwest and usually are much larger in size, in some cases greater than 10 cm in diameter.
My barefoot trimmer told me about the stones and I contacted the owner to see if she would send me the stones for a scientific study. You might be wondering why I was so interested in these stones. Several reasons: 1. As I mentioned, enteroliths are rarely seen in the eastern part of the U.S. 2. Like you, I am a horse owner and the presence of stones in your horse’s gut can be a serious health issue. and 3. I am a geologist with a background in chemistry so I am familiar with the microscopic techniques used to study rocks. After all, these are just special types of rocks (called concretions) that happened to be inside your horse’s body.
If you ever read about enteroliths, you know that they can cause colic episodes ranging from mild to severe, the latter usually requiring surgery to remove the stone. Since the owner’s horse had been recently experiencing colic episodes of unknown origin, this was an excellent opportunity to see if detailed analyses of the stones could reveal useful information about their origin and ways to prevent, or at least manage, their formation in the future. In this case, the small size of the stones was a distinct advantage in the analyses because thin slices (0.03 mm) through the entire stone could be mounted on one glass slide for microscopic studies. In addition, the whole stone could be easily sent to a chemical lab for analysis.
Horse intestinal stones are composed of struvite (NH4 Mg (PO4) 6 H2O) (where N=nitrogen, Mg=magnesium and P=phosphorous) and can only form in alkaline environments (high pH) with abundant ammonium ion NH4, Mg and P in colonic fluids. The chemical stability of struvite is well known in the scientific literature because struvite is a major problem in wastewater treatment plants, clogging pipes and attaching to impeller blades.
Because of their size, struvite stones are a major health issue in California and several other western states. Removal of large stones (12 cm or larger) that can obstruct or rupture the colon represented more than 25% of colic surgeries at UC Davis (Hassel et al. 2001). Some of the major risk factors cited in the literature include diet (high N, Mg and P feed), genetic predisposition related to breed, high pH of colonic fluids, and mineral content of water supply (Lloyd et al. 1987). Stones grow outward from a central core, or nidus (usually a foreign rock fragment), forming concentric bands similar to those observed in some natural concretions. There is usually an altered region around the nidus and an outer region consisting of well-crystallized struvite. As mentioned, reported occurrences of enteroliths in Eastern U.S. are rare (Taylor and Faure 1983).
The stones in this study are relatively small with an average diameter of ~1.5 cm and occur in a variety of shapes, including spherical, tetrahedral (or pyramidal) and ellipsoidal (see image above). A number of stones have one flattened side, indicating that they were grouped together and in contact in the colon along their flattened surfaces. All the stones were passed at the same time as the horse was fed in the stall.
For more information on this study refer to our full length scientific paper "Trace Elements in Struvite Equine Enteroliths: Concentration, Speciation and Influence of Diet" published in the Journal of Trace Elements in Medicine and Biology. A short summary also appears on theHorse.com.
Copyright George Lager, 2011-2023. All Rights Reserved (®)
My barefoot trimmer told me about the stones and I contacted the owner to see if she would send me the stones for a scientific study. You might be wondering why I was so interested in these stones. Several reasons: 1. As I mentioned, enteroliths are rarely seen in the eastern part of the U.S. 2. Like you, I am a horse owner and the presence of stones in your horse’s gut can be a serious health issue. and 3. I am a geologist with a background in chemistry so I am familiar with the microscopic techniques used to study rocks. After all, these are just special types of rocks (called concretions) that happened to be inside your horse’s body.
If you ever read about enteroliths, you know that they can cause colic episodes ranging from mild to severe, the latter usually requiring surgery to remove the stone. Since the owner’s horse had been recently experiencing colic episodes of unknown origin, this was an excellent opportunity to see if detailed analyses of the stones could reveal useful information about their origin and ways to prevent, or at least manage, their formation in the future. In this case, the small size of the stones was a distinct advantage in the analyses because thin slices (0.03 mm) through the entire stone could be mounted on one glass slide for microscopic studies. In addition, the whole stone could be easily sent to a chemical lab for analysis.
Horse intestinal stones are composed of struvite (NH4 Mg (PO4) 6 H2O) (where N=nitrogen, Mg=magnesium and P=phosphorous) and can only form in alkaline environments (high pH) with abundant ammonium ion NH4, Mg and P in colonic fluids. The chemical stability of struvite is well known in the scientific literature because struvite is a major problem in wastewater treatment plants, clogging pipes and attaching to impeller blades.
Because of their size, struvite stones are a major health issue in California and several other western states. Removal of large stones (12 cm or larger) that can obstruct or rupture the colon represented more than 25% of colic surgeries at UC Davis (Hassel et al. 2001). Some of the major risk factors cited in the literature include diet (high N, Mg and P feed), genetic predisposition related to breed, high pH of colonic fluids, and mineral content of water supply (Lloyd et al. 1987). Stones grow outward from a central core, or nidus (usually a foreign rock fragment), forming concentric bands similar to those observed in some natural concretions. There is usually an altered region around the nidus and an outer region consisting of well-crystallized struvite. As mentioned, reported occurrences of enteroliths in Eastern U.S. are rare (Taylor and Faure 1983).
The stones in this study are relatively small with an average diameter of ~1.5 cm and occur in a variety of shapes, including spherical, tetrahedral (or pyramidal) and ellipsoidal (see image above). A number of stones have one flattened side, indicating that they were grouped together and in contact in the colon along their flattened surfaces. All the stones were passed at the same time as the horse was fed in the stall.
For more information on this study refer to our full length scientific paper "Trace Elements in Struvite Equine Enteroliths: Concentration, Speciation and Influence of Diet" published in the Journal of Trace Elements in Medicine and Biology. A short summary also appears on theHorse.com.
Copyright George Lager, 2011-2023. All Rights Reserved (®)